In a receiving device in a wireless communication system, a sampling filter device is used for performing frequency conversion by discrete time charge sampling and filtering.
For example, Patent Document 1 describes a conventional sampling filter device. FIG. 12 shows the conventional sampling filter device described in Patent Document 1. The sampling filter device described in Patent Document 1 will be briefly described.
As shown in FIG. 12, a conventional sampling filter device 5 has a switch 2A, a switch 2B, an integrator 3, and a weight and sampling (W&S) element 6, and a control signal generator 7. Three processes of reset, sampling, and hold are respectively performed by a clock and an inversion clock, a W&S signal, and a reset signal generated from the control signal generator 7.
The filter characteristic of the sampling filter device is determined by a weight function. The weight function depends on a combination of the W&S element 6 and the W&S signal. The W&S signal corresponds to the three weight functions (constant, inclined, and Gaussian).
A current signal passing through the W&S element 6 is zero outside a sampling window and is weighted in accordance with the weight functions (constant, inclined, and Gaussian) inside the sampling window. Thus, output of the W&S element 6 is weighted by the W&S signal, whereby the filter characteristic can be changed.
JP-A-2003-510933 (page. 31, FIG. 2A)